CN101303257A - A Method for Measuring the Temperature of Long Gap Air Arc Plasma - Google Patents

Abstract

A method for measuring the temperature of long-gap air arc plasma relates to the field of thermal plasma temperature measurement. The temperature measurement method is based on the principle of spectral diagnosis of air arc plasma radiation, and the long-gap air arc image is captured by a calibrated color CCD high-speed image acquisition system with additional double narrow bandpass filters, and is stored as a data-uncompressed BMP format. Correct the pixel value of the arc color bitmap file under the two characteristic central wavelengths to the original data of the arc radiation intensity, obtain the radial light intensity distribution of the arc through Abel transformation, and then apply the colorimetric method of spectral relative intensity to calculate the arc radiation intensity Plasma projection temperature distribution or arc plasma temperature radial distribution to reconstruct the three-dimensional temperature field of long gap air arc plasma. The invention can accurately measure the temperature of open arc plasma with a length of several meters in the air, and provides an important plasma parameter for studying the microcosmic mechanism of long-gap air arc.

Description

A Method for Measuring the Temperature of Long Gap Air Arc Plasma

technical field

The invention relates to a method for measuring the temperature of long-gap air arc plasma, which belongs to the field of thermal plasma temperature measurement.

Background technique

The temperature of the air arc plasma is high, the heat capacity limit of the probe or thermocouple is difficult to meet the requirements, and the contact probe will interfere with the temperature field of the measured arc, so the non-contact method is usually used to measure the arc plasma temperature.

At present, infrared temperature measurement technology has been widely used in the field of non-contact temperature measurement. The continuous spectrum of air arc plasma radiation mainly covers the visible light region, while the response wavelength of the infrared thermal imager is far beyond the wavelength range of the arc plasma radiation. High, high radiation energy, may damage the infrared lens. In addition, the spectrometer, which obtains the arc temperature by diagnosing the spectral intensity or width of the line, is suitable for measuring the temperature of small arc plasmas, but it is difficult to measure the temperature of air open arc plasmas with a length of several meters. It can be seen that there are certain defects in using infrared thermal imager and spectrometer to measure the plasma temperature of long gap air arc.

With the development of photoelectric technology, computer technology and digital image processing technology, the non-contact temperature measurement technology based on color CCD image sensor has become a research hotspot in the field of high temperature detection due to the advantages of stable and reliable operation and high image definition of CCD. The chromaticity information contained in the CCD image and the principle of radiation temperature measurement are the important foundations of this temperature measurement technology. However, since the CCD response curve is limited by the bandwidth, and the plasma radiation signal will introduce errors after various transformations of the image acquisition system, the direct use of the colorimetric temperature measurement method has a large measurement error, and reducing the error is One of the main difficulties of this temperature measurement technique. At the same time, the color CCD image is the projection (integral value) of the three-dimensional radiation space of the arc on the two-dimensional CCD target surface. temperature field. Therefore, it is necessary to reconstruct the arc plasma temperature field with the help of mathematical conversion method.

Contents of the invention

In order to overcome the above-mentioned defects of the arc plasma temperature measurement technology, the object of the present invention is to provide a method for measuring the temperature of the long-gap air arc, so as to obtain the temperature distribution of the air arc plasma.

The technical solution adopted by the present invention to solve its technical problems is: a method for measuring the temperature of long-gap air arc plasma is based on the principle of spectral diagnosis of air arc plasma radiation, and is composed of double narrow bandpass filters and calibrated color CCD The high-speed image acquisition system captures long-gap air arc images and stores them in uncompressed BMP format. The pixel values of the arc color bitmap files at the two characteristic center wavelengths are corrected to the original data of the arc radiation intensity. Obtain the radial light intensity distribution of the arc, and then apply the colorimetric method of spectral relative intensity to calculate the arc plasma projection temperature distribution or the arc plasma temperature radial distribution, and reconstruct the three-dimensional temperature field of the long-gap air arc plasma.

The method that the present invention realizes above-mentioned technical scheme is:

The first step, optical preprocessing

Adding a neutral filter and two narrow-band filters with characteristic central wavelengths in front of the camera lens of the color CCD high-speed image acquisition system used to capture long-gap air arc images can eliminate the saturation distortion of the arc image and select the arc The incident light of the plasma radiation at the first wavelength λ1 and the second wavelength λ2 is transmitted through, so that the stored image signal meets the requirements of plasma spectrum diagnosis.

The second step is to calibrate the channel parameters of the color CCD image acquisition system

According to the spectral response characteristics of the color CCD high-speed image acquisition system, the channel parameters of the optically pretreated acquisition system at the first wavelength λ1 and the second wavelength λ2 are calibrated by using a standard radiation source. The basic principle is that the response value V of the color CCD and the spectral radiation intensity I satisfy: V=KI ^γ , and the channel parameters K and γ are the system conversion coefficient and the gamma correction coefficient respectively. The I of the standard radiation source at specific wavelengths and different temperatures is known, the response value V is measured, and the least squares method is used to fit these data to obtain the parameters K and γ.

The third step is to correct the arc plasma radiation intensity

The long-gap air arc image is captured by the optically preprocessed color CCD high-speed image acquisition system, which is stored in the BMP format without data compression, and the red and blue pixel values V corresponding to each point in the arc color bitmap file are read, and used to calibrate The channel parameters K and γ are corrected to the radiation intensity I of the arc plasma at the first wavelength λ1 and the second wavelength λ2.

The fourth step is to obtain the radial light intensity distribution

The long-gap air arc image is discretized along the axial direction. The spectral intensity of the micro-segment radiation in each arc cross-section satisfies cylindrical symmetry distribution, and the arc is an optically thin plasma. The optical thinness here refers to the absorption of radiation energy by the arc. The degree is far less than 1, so the measured projected light intensity can be converted into arc radial light intensity distribution by means of Abel transform.

The fifth step is to calculate the arc plasma temperature field

The main mechanism of the continuous spectrum of air arc plasma radiation is bremsstrahlung. Based on the relationship between the intensity of the arc bremsstrahlung spectrum and the plasma temperature, using the colorimetric method of the relative intensity of the spectrum, according to the arc at the first wavelength λ1 and the second wavelength λ2 Calculate the plasma projection temperature by lowering the corrected radiant light intensity, or use the radial light intensity distribution to obtain the radial temperature distribution of the arc plasma.

The expression for calculating the arc plasma projection temperature T is:

$\frac{\mathrm{<span\; class="notranslate">\; hc</span>}}{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; [</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="A20081011564900091.png"\; state="\{\{state\}\}">V</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; ln</span>}\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}$

In the formula, h is Planck’s constant, c is the speed of light, k is Boltzmann’s constant, V1 and V2 are the corresponding red and blue pixel values of the arc color image at the first wavelength λ1 and the second wavelength λ2, respectively, K1 and K2 are the conversion coefficients of the color CCD image acquisition system at the first wavelength λ1 and the second wavelength λ2 respectively, and γ1 and γ2 are the gamma corrections of the color CCD image acquisition system at the first wavelength λ1 and the second wavelength λ2 respectively coefficient;

The expression for obtaining the plasma radial temperature distribution T _i of the i-th point in the arc cross section is:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; hc</span>}}{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; [</span>\frac{\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span>}{\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; ln</span>}\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}$

In the formula, A _ij is the Abelian transformation coefficient, i, j=1, 2,..., N, N is the total number of points in the arc cross section, V1 _j and V2 _j are respectively the jth point in the arc cross section in the first The red and blue pixel values of the response at the wavelength λ1 and the second wavelength λ2 are used to calculate the radial distribution of the plasma temperature in the micro-section of each arc cross-section according to this expression, and finally all the radial temperature distributions are combined to form the entire arc Three-dimensional temperature field of plasma.

Owing to adopting above-mentioned technical scheme, the present invention has following advantage:

1. Give full play to the advantages of non-contact temperature measurement technology combined with color CCD high-speed camera and digital image processing, and make up for the defects of contact temperature measurement method, infrared thermal imager and spectrometer to measure the temperature of long-gap air arc plasma. The color CCD high-speed image acquisition system is used to capture long-gap air arc images with high image resolution and fast shooting speed. The pixel information in the uncompressed arc color bitmap is read to calculate the arc plasma temperature. The temperature measurement range is wide and the measurement accuracy is high. high. It can be seen that the present invention is simple and feasible, has good dynamic performance, high precision, great flexibility and engineering practical value.

2. The present invention uses a standard radiation source to calibrate the channel response parameters of the arc image acquisition system to ensure the authenticity and accuracy of the signal obtained by the arc plasma temperature measurement method.

3. The incident light of a specific wavelength is transmitted through the additional narrow-band filter, and the saturation distortion of the arc image is eliminated by the neutral filter, and the first wavelength λ1 and the second wavelength that do not overlap in the spectral response characteristics of the color CCD are selected. λ2 is the central wavelength of the narrow-band filter, which restores the red and blue pixels in the arc color bitmap file to the radiation intensity at the two characteristic wavelengths, effectively reducing the error caused by the calculation method.

4. The method of measuring arc plasma temperature based on the relationship between air arc plasma bremsstrahlung spectrum intensity and temperature reflects the physical nature of arc temperature, which is conducive to analyzing the internal characteristics of arc electron density, movement speed and so on from a microscopic point of view. The development mechanism of the air arc provides a powerful tool.

5. Discretize the long-gap air arc image, so that the light intensity distribution of each micro-section of the arc section satisfies columnar symmetry, use Abel transformation and colorimetry to calculate the radial temperature distribution of the arc plasma, and reconstruct the three-dimensional shape of the entire arc The temperature field not only obtains the temperature characteristics of the long-gap air arc plasma, but also avoids multiple unknown atomic parameters involved in the absolute light intensity temperature measurement method, and improves the measurement accuracy.

Description of drawings

Other characteristics and advantages of the present invention will be apparent in the following non-limiting exemplary embodiments with reference to the following drawings, which are:

Fig. 1 is a schematic structural diagram of a measuring system developed according to the present invention.

Fig. 2 is a flow chart of the calculation software of the present invention.

Detailed ways

Embodiments of the present invention will be described below in conjunction with the accompanying drawings and specific examples.

Fig. 1 is the overall structure of the measurement system made according to the present invention, which is mainly composed of long gap air arc generator, optical preprocessing device, color CCD high-speed image acquisition system and long gap air arc temperature calculation software. The long-gap air arc generator generates arc plasma to form an open arc with a length of 0.1-5m, a duration of 2s, and free movement in the atmosphere. The optical preprocessing device includes a neutral filter and two narrow-band filters, the neutral filter is optically neutral, the attenuation coefficient is constant in the full wavelength range, and the light intensity attenuation ratio is 8/1; the first The central wavelength λ1 of the narrow-band filter is 632.8nm, the half-peak bandwidth is 16nm, and the transmittance is 55%; the central wavelength λ2 of the second narrow-band filter is 441.6nm, the half-peak bandwidth is 10nm, and the transmittance is 70%. %. The color CCD high-speed image acquisition system is composed of a color CCD camera and an image acquisition device. The maximum image resolution is 1024×1024, and the shooting frame rate reaches 2000 frames per second, and the storage space is 8GB. The long-gap air arc temperature calculation software processes the arc image data to display the three-dimensional temperature field of the arc plasma. The calculation flow is shown in Figure 2. The channel parameters are set as follows: the channel conversion coefficient K1 corresponding to the first wavelength λ1 = 7.56×10 ^{- 5} , the gamma correction coefficient γ ₁ =0.595; the channel conversion coefficient K2 corresponding to the second wavelength λ2=0.0277, and the gamma correction coefficient γ ₂ =0.33.

The arc plasma radiation spectrum generated by the long-gap air arc generator is attenuated and filtered by the optical preprocessing device, so that the incident light at the first wavelength λ1 and the second wavelength λ2 enters the color CCD high-speed image acquisition system for imaging, and the arc color image It is transmitted to the computer through the data line, and the arc temperature calculation software reads the color bitmap file, and discretizes the space of the arc along the axial direction from the root of the upper arc, and then uses the channel parameters to convert the red, red, and red points of each arc cross-section micro-section The blue pixel is converted into the spectral intensity of the plasma radiation at the first wavelength λ1 and the second wavelength λ2, and the radial distribution of light intensity is obtained by Abel transformation, and the colorimetric method is used to calculate the arc plasma projection temperature or the arc cross-section plasma The radial temperature distribution of the arc body temperature, and the radial temperature distribution of the micro-segment of the arc cross-section is continuously increased downwards until the lower arc root, and finally the radial temperature distribution of all the micro-segments of the arc cross-section is combined to form the whole Three-dimensional temperature field of arc plasma.

The air arc plasma temperature is measured with a length of 180mm and a diameter of 6.6mm. The arc is in the vertical direction. The following table lists the radial distribution of the plasma temperature in the middle of the arc. Coordinates increase by step length 1mm upward, and coordinates decrease by step length -1mm downward.

Radial distribution of arc plasma temperature

The invention has been described in terms of preferred embodiments. Obviously, various modifications and substitutions will occur to others upon reading and understanding the above detailed specification. It is intended that this application be constructed to include all such modifications and substitutions as come within the scope of the appended claims or their equivalents.

Claims (2)

1, a kind of method of measuring long clearance air arc-plasma temperature is characterized in that this method measures long clearance air arc-plasma temperature by following steps:

The first step, the optics pre-service

The narrow band pass filter of additional neutral colour filter and two feature centre wavelengths is chosen the incident light of arc-plasma radiation under first wavelength X 1, second wavelength X 2 and is seen through before the camera lens of the colored CCD high-speed image sampling system that is used to take the long clearance air arc image;

In second step, demarcate colored CCD image capturing system channel parameters

Utilize calibrated radiation source that the pretreated channel parameters of colored CCD image capturing system under first wavelength X 1, second wavelength X 2 of optics demarcated, ultimate principle is to satisfy between the response V of colored CCD and the spectral radiance I: V=KI ^γ, channel parameters K, γ are respectively system's conversion coefficient and gamma correction coefficient, and the I of known standard radiation source under specific wavelength, different temperatures measures response V, adopts least square method that these data are carried out match and asks for parameter K and γ;

In the 3rd step, proofread and correct the arc-plasma radiation intensity

Employing is taken the long clearance air arc image through the pretreated colored CCD high-speed image sampling of optics system, be stored as data and do not have the BMP form of compression, read red, the blue pixel value V of each point response in the colored bitmap file of electric arc, utilize the channel parameters K and the γ that demarcate, it is the radiation intensity I of arc-plasma under first wavelength X 1, second wavelength X 2 that V is proofreaied and correct;

In the 4th step, ask for radially light distribution

The long clearance air arc image is carried out discretize vertically to be handled, the spectral intensity of little section radiation of each electric arc xsect satisfies post and is symmetrically distributed, and electric arc is optically thin plasma, by means of Abel transformation, the projection light intensity of being surveyed is converted to radially light distribution of electric arc;

In the 5th step, calculate the arc-plasma temperature field

Relation based on electric arc bremsstrahlung spectral intensity and plasma temperature, adopt colorimetric method, according to the arc radiation projection light intensity calculating plasma projection temperature after proofreading and correct, or utilize radially light distribution to ask for the plasma temperature radial distribution of little section of each electric arc xsect, at last all radial temperature profile are combined the three-dimensional temperature field that has just constituted whole arc-plasma.

2, the method for measurement long clearance air arc-plasma temperature as claimed in claim 1 is characterized in that:

The expression formula of wherein calculating arc-plasma projection temperature T is:

$T=\frac{\mathrm{hc}}{k}\&CenterDot;\frac{\frac{1}{\mathrm{\&lambda;}2}-\frac{1}{\mathrm{\&lambda;}1}}{\ln \left[\frac{{(V1/K1)}^{1/\mathrm{\&gamma;}1}}{{(V2/K2)}^{1/\mathrm{\&gamma;}2}}\right]+2\ln \frac{\mathrm{\&lambda;}1}{\mathrm{\&lambda;}2}}$

In the formula, h is a Planck's constant, c is the light velocity, k is a Boltzmann constant, V1, V2 are respectively red, the blue pixel value of electric arc coloured image in first wavelength X 1,2 times responses of second wavelength X, K1, K2 are respectively the conversion coefficient of colored CCD image capturing system under first wavelength X 1, second wavelength X 2, and γ 1, γ 2 are respectively the gamma correction coefficient of colored CCD image capturing system under first wavelength X 1, second wavelength X 2;

Wherein ask for the plasma radial Temperature Distribution T that i is ordered in the electric arc xsect _iExpression formula be:

$T_i=\frac{\mathrm{hc}}{k}\&CenterDot;\frac{\frac{1}{\mathrm{\&lambda;}2}-\frac{1}{\mathrm{\&lambda;}1}}{\ln \left[\frac{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}\left[A_{\mathrm{ij}}{({V1}_j/K1)}^{1/\mathrm{\&gamma;}1}\right]}{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}\left[A_{\mathrm{ij}}{({V2}_j/K2)}^{1/\mathrm{\&gamma;}2}\right]}\right]+2\ln \frac{\mathrm{\&lambda;}1}{\mathrm{\&lambda;}2}}$

In the formula, A _IjBe the Abel transformation coefficient, i, j=1,2 ..., N, N are always counting of electric arc xsect, V1 _j, V2 _jJ o'clock red, blue pixel value in the difference electric arc xsect in first wavelength X 1,2 times responses of second wavelength X.

Images